On Fri, Dec 12, 2014 at 9:08 PM, Arnd Bergmann <arnd@xxxxxxxx> wrote: > On Thursday 11 December 2014 16:05:04 Ray Jui wrote: >> + >> +- linux,gpio-base: >> + Base GPIO number of this controller >> + >> > > We've NAK'ed properties like this multiple times before, and it > doesn't get any better this time. What are you trying to achieve > here? I am to blame for suggesting using this property to Ray, and I am fully aware that this has been rejected before, but look at what people came with recently to palliate the lack of control over the GPIO number space for DT platforms: http://www.spinics.net/lists/arm-kernel/msg384847.html https://lkml.org/lkml/2014/12/10/133 Right now GPIO numbering for platforms using DT is a very inconsistent process, subject to change by the simple action of adjusting the value of ARCH_NR_GPIOS (which we did recently, btw), adding a new GPIO controller, or changing the probe order of devices. For users of the integer or sysfs interfaces, this results in GPIO numbers that change, and drivers and/or user-space programs that behave incorrectly. Ironically, the only way to have consistent numbers is to use the old platform files, where you can specify the base number of a gpio_chip. DT is actually probably not such a bad place to provide consistency in GPIO numbering. It has a global vision of the system layout, including all GPIO controllers and the number of GPIOs they include, and thus can make informed decisions. It provides a consistent result regardless of probe order. And allowing it to assign GPIO bases to controllers will free us from the nonsensical dependency of some arbitrary upper-bound for GPIO numbers that ARCH_NR_GPIOS imposes on us. Also about ARCH_NR_GPIOS, the plan is to eventually remove it since we don't need it anymore after the removal of the global gpio_descs array. This will again interfere with the numbering of GPIO chips that do not have a base number provided. Note that I don't really like this, either - but the problem is the GPIO integer interface. Until everyone has upgraded to gpiod and we have a replacement for the current sysfs interface (this will take a while) we have to cope with this. This issue has been bothering users for years, so this time I'd like to try and solve it the less ugly way. If there is a better solution, of course I'm all for it. -- To unsubscribe from this list: send the line "unsubscribe devicetree" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
